TOKYO (Reuters) - Australian Prime Minister Tony Abbott said on Sunday that he hoped for a quick conclusion to thorny free trade negotiations with Japan but suggested time might be needed to ensure conclusion of a "satisfactory" pact.

Ministers from both nations took part in a five-hour session on Saturday that ended well into the evening without agreement on several substantial issues, Australian Trade Minister Andrew Robb said. He termed the talks exhausting, but said progress had been made.

Abbott told reporters that he hoped a conclusion was near for the negotiations, launched in 2007.

"I am optimistic about the free trade negotiations, but they have been difficult negotiations," Abbott said, according to a transcript provided by the Australian government.

"This government is determined to bring them to a swift and satisfactory conclusion."

Japanese Agriculture, Forestry and Fisheries Minister Yoshimasa Hayashi, who also took part in Saturday's discussion, said there had been a "frank exchange of opinion" and he would be reporting on the progress to Prime Minister Shinzo Abe.

Abbott, who meets Abe on Monday, has set the free trade deal with Japan as a top priority, promising to drop tariffs on manufactured imports, including Japanese cars, while pushing Tokyo to cut tariffs on agricultural products, especially beef.

But he was cautious about the chances of clinching a deal during his visit, which lasts until Tuesday.

"I am hopeful, but not certain," he said. "There are still some final matters to be resolved and while we do want a swift conclusion, we want a satisfactory conclusion as well."

Robb said talks would resume on Sunday, but a Japanese Agriculture Ministry official said that had yet to be decided.

Japan is already Australia's biggest beef export market, both in volume and value terms, taking almost a third of all beef exported in 2012, according to Meat & Livestock Australia.

Failure by Japan and Australia to conclude a pact could ease U.S. worries that a trade deal with Australia prior to an agreement on the 12-nation Trans-Pacific Partnership (TPP) will give Australian exporters better access to Japan than their U.S. counterparts.

The United States urged Japan on Thursday to open up its farm and auto markets to overseas competition, with Trade Representative Michael Froman saying Tokyo's reluctance to lower trade barriers was holding up the TPP.

President Barack Obama, who had hoped to complete the TPP by the end of last year as a centerpiece of his push to expand the U.S. presence in Asia, is expected to press for a deal with Abe when he visits Japan this month.